The boss of a security firm has taken personal responsibility for the bomb scare which forced Manchester United's Old Trafford stadium to be evacuated on Sunday, costing the club millions in lost revenue.
The Red Devils' match with AFC Bournemouth was postponed when a suspicious device was discovered close to kick-off.
Chris Reid, managing director of Security Search Management & Solutions, which carried out a terror training drill at the stadium earlier in the week, said he took full responsibility for the blunder.
Speaking outside his home in Biggin Hill, south-east London, the retired Scotland Yard police officer said: "This mistake is entirely mine. I have to take full responsibility for leaving a training item behind on Wednesday."
He added: "I am absolutely devastated that a lapse in my working protocols has resulted in many people being disappointed, frightened and inconvenienced. Nothing I can say will rectify that."
Security Search Management & Solutions was hired by Deacons Canines to carry out practical training exercises at the stadium last week.
Mr Reid told reporters that after the exercise for five dog handlers he had checked a number of fake items into his bag, having previously recorded their position on a "trapping sheet".
He said: "Unfortunately an item that was placed in the male WC was not recovered, as I had a similar item that I had not used. I saw this and made the mistake in thinking that the item in the WC had been brought back when found by the attendees as had other items I had checked into the bag.
"This item concerned was a mock-up of a pipe bomb, it was approximately eight inches long, brass fittings at each end, a length of black flexible lead and a mobile phone taped to the pipe with black tape.
"The item had a small white label on it which said: 'Training aid if found contact ssms and my telephone number'."
He said he had been at home when events involved and watched it on television.
Mr Reid added that he had been contacted by people since saying "please carry on" with his work.
Asked it if had been a "blunder", he said: "I wouldn't say blunder. It's very difficult to say that, it's easy to say that and people will say, 'Yes it was'.
"However, there was something found and they dealt with it in the way they should have done, whether it should have been found sooner is completely another issue.
"It would be obvious to say yes they should have found it. But I don't know - the rooms may have been locked after I left, without being checked, and why should they be?"
United's executive vice-chairman Ed Woodward had earlier revealed that the device had been recorded as having been removed.
Manchester's police and crime commissioner Tony Lloyd said that the Red Devils needed to be "up front" with answers about the "shambolic" security scare at Old Trafford.
Mr Lloyd, who is also the mayor of Greater Manchester, said the club's reputation and public safety had come under scrutiny after Sunday's evacuation.
He said: "'Fiasco' is the right word. It was shambolic.
"Of course, United are a huge organisation. It wasn't, I think, the fact they're the world's richest club - that they are.
"It was the fact that the security had missed something that in the end ought to have been found."
United are currently in sixth and could only qualify for the Champions League if they win by 19 goals - a Premier League record.